1. Field of the Invention
The present invention relates to a broadcasting communication system for transmitting and receiving broadcast service data using one Radio Frequency (RF). More particularly, the present invention relates to a method and apparatus for transmitting and receiving a frame composed of a plurality of broadcast services in a broadcasting communication system, a method for configuring the frame, and the frame thereof.
2. Description of the Related Art
In the 21st century's information society, broadcasting communication services are entering the era of the digital, multi-channel, broadband and high-quality broadcasting and communication. Particularly, with the recent increasing popularization of high-definition digital television, Portable Multimedia Player (PMP) and portable broadcasting devices, digital broadcasting services also increasingly need to support various reception schemes.
To meet the needs, Digital Video Broadcasting-Terrestrial 2 (DVB-T2), which is the European 2nd generation terrestrial digital broadcasting standard, is pushing ahead with standardization for each of three reception schemes. The first is a reception scheme of recycling the conventional household digital reception antennas. The second is a reception scheme using multiple antennas for capacity improvement. The third is a reception scheme for portable mobile terminals. Compared with DVB-Terrestrial/Handheld (DVB-T/H), which is the 1st generation terrestrial digital broadcasting standard and considers only two reception schemes of a fixed reception scheme and a mobile reception scheme, the DVB-T2 additionally considers the reception scheme of using multiple antennas. The DVB-T2 standard does this by considering, as its main standardization work, an operation of changing a physical layer structure and control information based on the physical layer structure.
In the physical layer structure, a control channel refers to a channel that transmits a control message for a transmission scheme in the physical layer. If the basic unit of a transmission signal is defined as a frame, one frame can be composed of a plurality of services and include a service index, location information, modulation scheme/coding rate, and cell identifier (ID) for each service. The control channel can be transmitted independently of a data channel in every frame, since the service configuration and its associated information can vary frame by frame. Since demodulation for the control channel should be performed first in order for a terminal to receive a service channel, the control channel should be situated first in the frame. Following the control channel is a plurality of services. In the following description, the control channel in the broadcasting system will be referred to as a P2 preamble.
FIG. 1 is a diagram illustrating a scheme of transmitting and receiving broadcast services in a Fixed Frequency (FF) mode indicating the conventional 1st generation broadcasting system.
Referring to FIG. 1, a transmitter 102 transmits different broadcast services at their associated multiple RFs, and a receiver 104 receives its desired service by tuning to an RF on which the desired service is transmitted. For example, when the receiver 104 wants to receive a service 1, the receiver 104 tunes its reception module to RF1, acquires information such as location information and modulation/coding scheme for the service 1 through a P2 preamble, and then demodulates the service 1.
As can be seen in FIG. 1, as regards a plurality of services constituting one frame in an arbitrary RF channel, each service's length in the time domain is different since each service has a different transmission data rate. In this case, a service having a high transmission data rate can be considered to undergo sufficient time diversity since it has a long transmission period in the time domain, whereas a service having a low transmission data rate cannot be considered to obtain a sufficient diversity gain because it has a very short transmission period. In particular, as the broadcasting system is very susceptible to impulse noises, multiple Orthogonal Frequency Division Multiplexing (OFDM) symbols, rather than one OFDM symbol, are apt to be damaged in the time domain. Since the service having the low transmission data rate is composed of fewer symbols, most data corresponding to the service may be damaged when an impulse noise occurs, causing a possible case in which the corresponding service cannot be demodulated at all in the frame.
Therefore, in order to allow a transmission service to obtain a time diversity gain, each service can be sliced into more than two small services in the time domain. The sliced sub-services having a small size will be referred to herein as sub-slices. When such service slicing is performed, an increase in the number of service slicings causes an increase in diversity gain that can be obtained in the time domain. Generally, up to several hundred service slicings can be considered to acquire a very high diversity gain.
In this specification, with reference to FIGS. 2A and 2B, a description will be made of a method for configuring a frame using the service slicing in a conventional broadcasting communication system.
FIG. 2A is a diagram illustrating a conventional frame structure in which 4 logical services are arranged.
Referring to FIG. 2A, a conventional frame structure can be seen in which 4 logical services are disposed. When their service indexes are given as 1, 2, 3 and 4, the 4 services can be arranged in the frame in an arbitrary order. In the example of FIG. 2A, the services are arranged in ascending order of the index value. Further, time periods of the services are denoted by T1, T2, T3, and T4, respectively.
In order to physically map the services, which are logically configured in one frame, to a frame through service slicing, each service should undergo service slicing. For example, if each service is divided into 4 sub-slices, a transmission period for each service in the time domain occupied by the corresponding service should be divided by 4 as shown in FIG. 2A. Therefore, the services each have 4 sub-slices having sub-slice periods T1/4, T2/4, T3/4, and T4/4. As a result, a total of 16 sub-slices are generated for the 4 services that should be transmitted over the frame.
FIG. 2B is a diagram illustrating a conventional frame in which services are physically arranged, each of which consists of sub-slices by service slicing.
Referring to FIG. 2B, 4 sub-slices constituting one service should be spaced as far away as possible to achieve time diversity. Since the services each are configured with the same number of sub-slices, the distance between sub-slices belonging to the same service is constant. That is to say, since each service is sliced into 4 sub-slices, an interval, or distance, between sub-slices belonging to the same service becomes a value obtained by dividing the total frame period TF by 4, so the sub-slices have a uniform interval. For example, FIG. 2B shows an interval TF/4 between 4 sub-slices 1-1, 1-2, 1-3 and 1-4 (where former numerals represent service indexes while latter numerals represent sub-slice indexes) belonging to the first service. Since the distance between sub-slices belonging to the same service is equal, the order of sub-slices for each service, arranged in the first TF/4 period, is equally repeated every TF/4.
As described above, one purpose of using the method for mapping services in a frame based on the service slicing is for obtaining diversity gain for the services transmitted in one frame including a service having a low transmission data rate.
Since a corresponding service in one frame is composed of multiple sub-slices, a receiver needs to perform demodulation as many times as the number of sub-slices in order to receive a target service it should receive. In other words, assuming that each service consists of 4 sub-slices as shown in FIGS. 2A and 2B, because a receiving terminal should perform demodulation 4 times for a one-frame time period, switching between demodulation and non-demodulation happens four times.
However, when the reception operation is considered in a mobile terminal as opposed to a fixed terminal, an operation of performing demodulation for a sub-slice period and not performing demodulation until the next sub-slice is received, is repeated as many times as the number of sub-slices. Such an operation increases the power that the mobile terminal should consume, and causes a heavy burden in terms of power consumption. That is, from the standpoint of the mobile terminal, the service slicing operation that is used to obtain a time diversity gain requires heavy power consumption for the battery, causing a power problem.
Therefore, in considering the fixed terminal, it is preferable to perform service slicing as many times as possible. Conversely, for the mobile terminal, it is preferable to continuously transmit one service in the time domain without service slicing (i.e. the number of sub-slices corresponding to one service is one), or to carry out service slicing as few times as possible.
However, when services in a frame are physically mapped using various types of the number of service slicings (e.g. a service for one fixed terminal is composed of 100 sub-slices while a service for one mobile terminal consists of 4 sub-slices) in order to consider both the fixed terminal and the mobile terminal, the interval between sub-slices belonging to the same service may not be constant.
This means that for all sub-slices for the fixed and mobile terminals, a base station should signal all their location information in a frame. For instance, assume that an overhead of 20 bits is needed to indicate location information in a frame, 4 services for a fixed terminal and 1 service for a mobile terminal are transmitted through one frame, a service for the fixed terminal is mapped to 4 sub-slices, and a service for the mobile terminal is mapped to one sub-slice. In this case, as a total of 17 sub-slices exist in the frame, signaling for the total of 17 locations requires 20*17=340 bits, causing an increase in the signaling overhead.
Accordingly, there is a need for an apparatus and method for improving reception performance of a broadcast service.